feat(email-to-pdf): add inline images, clickable links, and embedded attachments

- Add CID inline image support via base64 data URI replacement
- Implement clickable link extraction from HTML anchors using regex
- Embed email attachments into PDF using pymupdf embfile_add
- Reduce font sizes for more compact PDF output (18px subject, 12px body)
- Format date with timezone (UTC+HH:MM) while preserving original time
- Clean email address formatting (Name (email) instead of <brackets>)
- Add UI options: page size selector, CC/BCC toggle, attachments toggle

index.html

@@ -95,8 +95,6 @@
     />
     <link rel="icon" href="/favicon.ico" sizes="32x32" />
 
-    <!-- i18n: hreflang tags for SEO -->
-
     <link href="src/css/styles.css" rel="stylesheet" />
   </head>